This invention relates to a probe for a printed-circuit testing device, said probe being intended to permit testing of either bare circuits or circuits equipped with components. When produced on a large scale by means of semi-automatic or fully automatic operations, printed circuits have to be checked prior to delivery or use with a view to ensuring good operating conditions or on the contrary to detecting any possible fault locations. As a general rule, inspection and testing operations are performed automatically by means of test instruments or devices for checking up to 4000 points on these circuits, the tests being carried out in time intervals of relatively short duration, namely of the order of 5 seconds or sometimes less.
A printed-circuit testing device is usually made up of three sections, namely a base system, measuring heads and a suction unit. The respective functions of these different sections are as follows: the base system provides an interface between the measuring heads and a wiring tester; the measuring heads provide the interface between the printed circuits to be tested and the measuring system and the suction unit is intended to produce a partial vacuum within the device in order to apply the printed circuit to be tested against the measuring head and to ensure a better contact between the circuit and the probes carried by the measuring head. The design function of said probes is to establish an electrical connection between one point of the printed circuit on which the probe head is brought to bear and the wiring tester.
Testing of printed circuits must be practicable in the case of either a bare circuit or a circuit equipped with components. At the present time, however, it is not possible to employ a single probe in order to carry out both these two tests under good conditions. Whereas the probes which are employed for testing bare circuits and which have a head consisting of a point are capable of establishing a contact with the metallized holes of the circuit, this will no longer be the case with equipped circuits in which component connection strips which are endowed with a certain degree of flexibility cannot be gripped by the probe head; there will either be no contact or a poor contact and the test will be inconclusive. In order to test an equipped circuit, it will therefore be necessary to change the probes. In some designs, the probe heads employed for testing printed circuits equipped with components are either grooved or crown-shaped. In this case, although gripping of connection strips is achieved under more satisfactory conditions and it is possible to establish a better contact with solder-spot connections, this no longer holds true if it is desired to change-over to testing of a bare circuit since the probe head cannot come into contact with a metallized hole. Furthermore, since the probe head has a certain surface area in this case, there is a potential danger of establishing a contact both with the collar which surrounds the orifice of a metallized hole and with the tracks which are located in the immediate vicinity, with the result that there is an attendant danger of short-circuits.